This invention relates to devices which detect and/or treat tachyarrhythmias (rapid heart rhythms), and more specifically, to the operation of arrhythmia prevention pacing modes which vary the pacing rate on a beat by beat basis in such devices.
In addition to delivery of pacing pulses to terminate tachyarrhythmias and to treat bradycardias, a number of pacing modes have been recently developed which are intended to prevent the occurrence of tachyarrhythmias. These pacing modalities can generally be described as xe2x80x9ctachyarrhythmia prevention pacing modesxe2x80x9d, and include, for example, ventricular rate stabilization pacing as disclosed in U.S. Pat. No. 4,941,471 issued to Mehra, an improved version of ventricular rate stabilization pacing as disclosed in U.S. Pat. No. 5,545,185, issued to Denker et al, atrial rate stabilization pacing as disclosed in U.S. Pat. No. 5,846,263 issued to Peterson et al, and an atrial pacing preference modality as disclosed in U.S. Pat. No. 5,522,859 issued to Hess et al., all of which are incorporated herein by reference in their entireties.
The tachyarrhythmia prevention pacing modalities described in the above patents attempt to prevent the occurrence of tachyarrhythmias by varying the interval between pacing pulses in a chamber of the heart, either the atrium or the ventricle, on a beat by beat basis. When incorporated in implantable devices, these pacing prevention modes are typically activated singly, as the proposed beat to beat change in pacing rate may differ substantially from one pacing modality to another. While it has been proposed to provide a pacemaker which automatically selects which of a number of available tachyarrhythmia prevention pacing modes is employed, as described in U.S. patent application Ser. No. 09/135,331, filed Aug. 17, 1998 by Mehra et al, and incorporated herein by reference in its entirety, the prior art typically envisions that only a single tachyarrhythmia prevention pacing mode will be operative at any one time.
The present invention is directed toward providing a pacemaker in which multiple tachyarrhythmia prevention pacing modes may be simultaneously active, with the escape intervals for each mode being calculated and updated on a beat by beat basis, with the device selecting the most appropriate of the various calculated escape intervals for use during the next cardiac cycle. The device makes the decision as to which tachyarrhythmia prevention pacing modality is employed to control the escape interval of the current cardiac cycle in order that the more appropriate method for calculating the escape interval, based on the present condition of the patient, may be selected.
A variety of criteria may be employed in order to select between the escape intervals provided by the tachyarrhythmia prevention pacing modes concurrently in operation. For example, one simple implementation would be to simply select the shorter of the calculated escape intervals. An alternative mechanism might be to employ the escape interval which represents the smallest net beat to beat change of escape interval. Yet an additional alternative would be to employ the calculated pacing rate of one of the pacing modalities preferentially, unless it differs by greater than a predetermined amount or percentage from the escape interval calculated by the second pacing modality, in which case the escape interval calculated by the second pacing modality would be employed. An additional alternative mechanism for selecting between the escape intervals provided by the two facing modalities would be to employ a criterion based decision methodology, in which selection of pacing escape interval is determined as a function of the operational history of the device, looking to previous frequencies of occurrences of arrhythmias associated with the various pacing modalities in situations similar to that associated with the present escape interval. In the context of the present invention, it is envisioned that the available arrhythmia prevention pacing modalities, in preferred embodiments, may be automatically disabled in response to detection or pre-detection of tachyarrhythmias in the atria and/or ventricles of the heart. The criteria employed for disabling the arrhythmia prevention pacing modalities may be the same for each pacing modality or may differ.
One of the tachyarrhythmia prevention pacing modes provided by the present invention may be an Atrial Rate Stabilization pacing mode, as described in U.S. Pat. No. 5,843,263, issued to Peterson et al, incorporated herein by reference in its entirety. The Atrial Rate Stabilization (ARS) pacing mode is similar in some respects to that disclosed in U.S. Pat. No. 5,713,929, issued to Mehra et al, but particularly adapted to controlling atrial pacing rate. In this pacing modality, the pacemaker-defined escape interval following a paced or sensed beat is set equal to the interval separating the paced or sensed beat from the preceding paced or sensed beat (preceding heart cycle length), plus an increment. The increment may be either a fixed value or more preferably a value which varies as a function of the preceding cycle length. This pacing modality eliminates the pauses following premature atrial beats and gradually returns the atrial cycle to its programmed or otherwise determined base value.
A second tachyarrhythmia prevention pacing mode provided by the present invention may be an Atrial Pacing Preference mode (APP), as described in U.S. Pat. No. 5,522,859 issued to Hess et al., incorporated herein by reference in its entirety. This pacing modality is adapted to deliver atrial pacing pulses at just above the sinus rate, in order to eliminate or reduce the frequency of atrial tachycardia and atrial fibrillation. In general, the sinus rate is a rate determined by periodically or at predetermined times reducing the pacing rate until a natural rhythm of heart beats is found in the atrium, (i.e., sinus node generated atrial depolarizations) and then increasing the paced rate again by a predetermined amount. When enabled, this pacing modality operates by initially decreasing the atrial escape interval on consecutive beats until atrial pacing is established. After a programmable number of beats, the escape interval is be increased incrementally until intrinsic atrial activity is once again discovered. When atrial intrinsic depolarizations are sensed, then the escape interval is decreased in increments until consistent atrial pacing is restored.